1. Background of the Invention
The present invention is related to an improvement of an on-line moisture measuring apparatus wherein powdered or granular materials including inorganic materials such as pelletized resins and ceramics are automatically sampled and the moisture content thereof is automatically measured.
2. Prior Art
Generally, keeping moisture content of resin materials constant in order to maintain good quality of the resin products created a most important problem because with an inappropriate moisture content of the resin materials to be supplied into a molding machine defects such as a silver line or void are caused. Therefore, resin materials are usually dried by the use of a hopper dryer prior to being supplied into the molding machine. However, before the resin materials are fed into the hopper dryer, they are apt to absorb moisture in the air while being stored in a silo or a tank of intermediate stage for a fixed period of time after a kraft bag or a flexible container which is used to carry resin materials is opened. Accordingly a fixed heating temperature and a fixed heating time are set for the hopper dryer, which are based on an estimated moisture content of the resin materials. But such a conventional method for drying resin materials by the use of a hopper dryer leaves further room for improvement in saving labor.
On the other hand, a titration analysis using a Karl Fischer reagent has been conventionally known as a method for titrating and analyzing the moisture content of resin materials. A moisture meter has been developed in which titration analysis by a Karl Fischer reagent is performed by means of a coulometric method, a volumetric method, and a colorimetric method, whereby a high accuracy can be obtained.
Considering the above, an on-line moisture control method and the system has been proposed by the present inventors in JP-A-3-63558 (U.S. patent application Ser. No. 557,865 now U.S. Pat. No. 5,146,692 and EPC Patent Publication 0411848) wherein powdered or granular materials such as resin materials are automatically sampled and their moisture content is measured by means of a Karl Fischer reagent employing inert gas as a carrier gas.
However, the invention employed inert gas such as nitrogen gas as a carrier gas for a Karl Fischer reagent. Therefore, a gas cylinder containing inert gas should be regularly exchanged and pipings were increased and complexed. Furthermore, a gas cylinder should be frequently exchanged when the system was used many times and consequently the consumption of inert gas increased. Therefore, the invention leaves further room for improvement from the view point of maintenance.